1. Field of the Invention:
This invention relates to a method of grinding a workpiece with a cylindrical portion and a couple of shoulder portions formed contiguously to the cylindrical portion through a curved portion, like crank shaft pins or journals.
2. Description of the Prior Art:
As shown in FIG. 1, a crank shaft pin or journal generally has a straight cylindrical portion CP and shoulder portions SP which are formed on opposite sides of and connected to the cylindrical portion CP through rounded corner portions RCP. For grinding such a pin or journal, it has been the conventional practice to employ a full-form grinding wheel g with a shape corresponding to that of a machining portion of a workpiece, forming the cylindrical and shoulder portions CP and SP by plunge grinding.
This grinding method requires to provide various full-shape grinding wheels g according to the kinds of crank shafts to be machined. Besides, the plunge grinding by a full-shape grinding wheel g involves a greater amount of grinding per unit grinding width S at the cylindrical and shoulder portions CP and SP, so that the rounded corner portions RCP which are formed at the opposite axial ends of the circumference of the full-shape grinding wheel g undergo considerable abrasive wear, as a result inviting deteriorations in grinding accuracy of the shape of the rounded corner portions adjacent the shoulder portions SP. In order to avoid this problem, tooling for re-shaping the rounded corner portions is necessitated although the circumferential surface of the full-shape grinding wheel g is still usable. However, in view of the recent trend of using expensive CBN (cubic boron nitride) grinding wheels for the purpose of enhancing the efficiency of grinding operation, it is extremely disadvantageous from the standpoint of machining cost to provide such grinding wheels in a large variety or to leave a large allowance for tooling.